(a) Field of the Invention
This invention generally relates to a system for controlling the pitch of boat propeller blades. More particularly, but not by way of limitation, to a variable pitch propeller, to a system that allows the user of a propeller driven boat to vary the pitch on the propeller to vary the amount of advancement of the screw through the water, while maintaining constant propeller speed (revolutions per minute).
(b) Background Art
The advantages of variable pitch propellers have long been recognized, particularly in applications dealing with watercraft. An important advantage that is gained from adjusting the pitch of the propeller blades is that the more effective use of the engine""s horsepower can be made. More specifically, to initiate motion of the boat, a low pitch angle is desired to allow the engine to develop the necessary revolutions per minute (RPMS) and power output to provide the needed thrust and acceleration to accelerate the boat. Once a desired speed is reached, the angle of the blades may then be adjusted to provide the needed thrust to maintain the speed of the boat while allowing the blades to self adjust to maintaint the optimal pitch angle for a given boat speed.
An important, highly desired, characteristic of a propeller system is that it provide only the amount of thrust needed to maintain the desired boat speed. Thus, while accelerating the propeller system would provide a great deal of thrust, and while cruising at a constant speed the propeller would provide the power needed to overcome the losses associated with friction or drag. Additionally, at higher speeds the advancement of the boat per turn of the screw is greater. Therefore, it follows that it is desirable to increase the pitch of the blades at higher speeds to accommodate for the greater distance advanced with each turn. Thus, it is desired to reduce the engine RPM when possible to do so while maintaining boat velocity, and thus optimizing fuel economy for a given boat velocity.
Still further, since the losses at a constant speed are likely to stay constant, it would appear that it is desirable to provide a propeller system that is sensitive to the amount of thrust needed, and that would adjust the amount of pitch on the propeller in proportion to the required thrust.
Another desired feature that is needed in variable pitch propellers is that the mechanism used to adjust the pitch of the blades should adjust the pitch angle of each blade in a manner that results in all blades providing substantially the same helix or screw angle. Maintaining the same helix or screw angle on each blade allows even distribution of the thrust load on each of the blades.
Additionally, it is highly desirable that the mechanism used to pivot the blades be simple, reliable, and unobtrusive. The expense associated with the manufacture and maintenance of complicated variable pitch boat propeller mechanisms has limited the use of these propellers to applications where performance carries a higher priority than cost. This has meant the use of these propellers has been limited to military craft or similar high performance water craft.
Yet another problem associated with the adoption of propeller systems which use variable pitch propellers is that these systems will typically require that the user discard the entire drive system of boat, including drive shafts and exhaust systems used with the existing motor. This is a serious limitation that has prevented wide spread use of variable pitch propellers because the increase in performance provided by the ability to vary the pitch has yet to be provided in a cost effective manner that would justify the replacement of an entire drive system on an existing boat drive mechanism.
Known examples of variable pitch propellers include the mechanism shown in U.S. Pat. No. 5,366,343 to Muller. Muller teaches a variable pitch propeller that can be mounted on the shaft of a non-variable pitch drive motor which can be modified to accommodates the mechanisms for operating this system. In other words, the existing device must accommodate an external actuator mechanism that moves the Muller propeller""s blades to a desired angle. This arrangement exemplifies the problems associated with many known variable pitch systems. The external actuator increases drag and complexity of the system. Additionally, the Muller system is designed to completely detach the hydraulic actuation system from the propeller. This eliminates or greatly reduces the coupling or association of the thrust on the propeller and the pressure in the hydraulic system of the mechanism.
Similar approaches can be found in many examples of known deices. For example the systems taught in U.S. Pat. No. 4,872,811 to Cavallaro et al., U.S. Pat. No. 4,822,243 to Poucher, U.S. Pat. No. 4,563,940 to Wuhrer, U.S. Pat. No. 4,952,083 to Kuehl, U.S. Pat. No. 4,907,992 to Cavallaro et al., U.S. Pat. No. 4,880,402 to Muller, U.S. Pat. No. 4,744,727 to Muller, U.S. Pat. No. 5,836,743 to Carvalho et al.
Thus, a review of known devices reveals that there remains a need for a simple variable pitch mechanism for use with boat propeller systems.
Importantly, there remains a need for a variable pitch boat propeller system that is sensitive or responsive to the amount of load needed for maintaining the speed of the boat, and thus a system that automatically adjusts the pitch of the propeller to increase the thrust as needed to maintain a constant boat speed.
There remains a need for a simple adjustable pitch boat propeller system that can be used with a commercially available marine drive unit which was originally designed for accepting a fixed blade propeller.
Still further, there remains a need for a variable pitch propeller system that is robust, and uses few moving parts.
It has been discovered that the problems left unanswered by known art can be solved by providing an adjustable pitch propeller system which includes:
an annular hub;
an annular piston that has been adapted for moving within the annular hub; and
at least two blades which are pivotally mounted on the hub and connected to the annular piston, so that movements of the annular piston within the annular hub produce simultaneous movements of the blades.
According to a highly preferred embodiment of the invention, each of the blades is connected to the annular piston by way of a link or connecting rod. The link is pivotally connected to the annular piston at one end and pivotally connected to a blade at the other end. According to a highly preferred example of the invention, it is contemplated that the connection between each of the blades and the link will include a blade angle adjustment plug. The adjustment plug will allow the user to change the effective length of the linkage to vary the starting pitch of each of the blades.
Additionally, it is important to note that it has been discovered that the annular hub allows mounting of the disclosed system on the propeller shaft of a marine drive unit with little or no modification of the output shaft of the motor. According to a highly preferred embodiment of the invention the annular piston is powered or moved in one direction by the exertion of hydraulic pressure from a governor mechanism. The governor mechanism allows the user to set the hydraulic pressure against the annular piston at a desired level. Because the piston is connected to the blades by way of the linkage, the force of the water against the moving blade will transmit the resulting thrust related force against the blade on to the piston through the linkage. This thrust related force must be balanced by the hydraulic pressure imposed on the piston by way of the governor mechanism. Thus, it will be appreciated that the pitch of the blades will be determined by the linkage geometry and the hydraulic pressure against the annular piston as set by the governor. Of course, this relation between the pitch of the blades and pressure set by the governor is not applicable beyond the length of travel of the piston. Thus, if very low hydraulic pressure is applied to the piston while the propeller is turning, the force of the water against the blades will cause the blades to return to the lowest pitch position, forcing the annular piston into the hub until the bottom or end of the annular piston""s travel is reached. Maximum pitch is achieved when the annular piston reaches the opposite end of the stroke travel.
Thus, it will be understood that the disclosed invention solves problems associated with known adjustable pitch boat propellers or screws by providing constant adjustment of the blade pitch in proportion to the speed, and hence water induced load, of the propeller. Accordingly, the disclosed invention will allow the user to maintain constant boat speed by adjusting the pressure provided by the governor in addition to varying engine RPM (revolutions per minute).
Still further, it will be understood that the disclosed system provides a simple, robust, mechanism that uses structure that exists on most marine drive units with little or no modification of these drive units.
It should also be understood that while the above and other advantages and results of the present invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings, showing the contemplated novel construction, combinations and elements as herein described, and more particularly defined by the appended claims, it should be clearly understood that changes in the precise embodiments of the herein disclosed invention are meant to be included within the scope of the claims, except insofar as they may be precluded by the prior art.